C. Owen Plank Extension Agronomist The University of Georgia C. Owen Plank Extension Agronomist The...
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www.ugaextension.comwww.ugaextension.com
C. Owen PlankC. Owen PlankExtension Agronomist
The University of Georgia
C. Owen PlankC. Owen PlankExtension Agronomist
The University of Georgia
Learning Objectives
• Soil components and their relative Soil components and their relative proportion in soilsproportion in soils
• Texture of a soil & influence of texture Texture of a soil & influence of texture on plant growthon plant growth
• Soil compaction, how to alleviate it, & Soil compaction, how to alleviate it, & how compaction affects plant growthhow compaction affects plant growth..
• Soil organisms & effect on the Soil organisms & effect on the chemical and physical properties of chemical and physical properties of soilsoil
• Importance of soil organic matterImportance of soil organic matter
• How different soil amendments affect How different soil amendments affect the structure, texture, and pH of soilsthe structure, texture, and pH of soils
• Colloids, CEC, cations, and anions and how they affect plant nutrition
• Why pH is such an important factor in nutrient uptake and plant nutrition and how changing pH affects different soil properties
• Essential elements required for plant growth and the different inorganic and organic fertilizer sources of each.
What Is Soil?What Is Soil?What Is Soil?What Is Soil?
Webster Defines Soil As…..
• The upper layer of the earth that may be dug or plowed and in which plants grow
• However, to soil scientists the definition is more complex
• It may have different meanings to different people
FarmerFarmer
ForesterForester
HorticulturistHorticulturist
Golf Course
Superintendent
Golf Course
Superintendent
EngineerEngineer
Know Your Soil!Know Your Soil!Know Your Soil!Know Your Soil!
Soil Composition - Volume BasisSoil Composition - Volume Basis
Organic Matter
5%
Water25%
Air25%
Mineral Matter45%
Soil Profile
Permanent Soil PropertiesPermanent Soil Properties
• Texture
• Thickness of topsoil
• Thickness of subsoil
• Certain Chemical Properties
Changeable Soil PropertiesChangeable Soil Properties
• Soil Structure
• Soil Organic Matter
• Soil Color
• Soil pH (Acidity)
• Soil Nutrient Levels
SOIL TEXTURESOIL TEXTURE
Soil TextureSoil Texture
• Soil texture refers to the relative proportions of sand, silt, and clay in a soil
• 12 textural classes
• Loam is considered to be ideal texture for growth of plants
• Difficult to alter soil texture on large scale
Importance of Soil TextureImportance of Soil Texture• Influences pore size and pore space
- large pores - air- small pores - water- sandy soils have larger pores, less surface area, and water drains more freely compared to clay soils
• Influences a soils water holding capacity- fine textured soils have more and smaller
pores- hold more water than sandy soils- also hold water more tightly
Source: Brady & Weil
Soil StructureSoil Structure
• Manner in which soil particles are arranged together
• Particles in sandy soils may remain independent of each other
- single grain texture
• Particles in fine textured soils are arranged in a definite manner to form stable aggregates
Importance of Soil StructureImportance of Soil Structure
• Improves air & water relationships
• Improves root penetration
• Improves water infiltration
• Reduces erosion
• Ease of tillage
• Reduces crusting
Maintaining Soil StructureMaintaining Soil Structure
• Add Organic Matter
• Till Soil When Moist– Not Too Wet or Too Dry
• Grow Grasses
• Grow Cover Crops– Keeps Soil Protected from Rain, etc.
• Restrict Traffic
Relative Compacting Effects of Soils by Different Agencies
Relative Compacting Effects of Soils by Different Agencies
Pressure, Lb.Item Per Sq. Inch
Man (150 pounds) 6Crawler Tractor 12Farm Tractor 20Cattle 24Trucks 50 –100Rototiller (garden) 107 – 750
Pressure, Lb.Item Per Sq. Inch
Man (150 pounds) 6Crawler Tractor 12Farm Tractor 20Cattle 24Trucks 50 –100Rototiller (garden) 107 – 750
Soil ColorSoil Color
• Many different soil colors
• Give important clues about soils chemical and physical environment
Soil Variation
Organic MatterOrganic Matter
• Improves soil physical condition
• Reduces erosion
• Improves water infiltration
• Improves water holding capacity
• Increases soil cation exchange capacity
• Source of nutrients
Organic Matter Organic Matter • Contains varying amounts of all the essential
nutrient elements
- e.g. ~ 5% Nitrogen
• Serves as important storehouse of elements such as nitrogen and sulfur
• Nutrient elements contained in freshly added organic matter are not immediately available to plants
• Residues must be decomposed into humus, and nutrients released in ionic form
Humus Formation
Carbohydrates CelluloseProteinsLignin
Residues
Humus
CO2
ProteinLignin
NitrogenUptake
SoilSoilMicroorganismsMicroorganisms
• BacteriaBacteria• FungiFungi• ActinomycetesActinomycetes• AlgaeAlgae
SoilSoilMicroorganismsMicroorganisms
• BacteriaBacteria• FungiFungi• ActinomycetesActinomycetes• AlgaeAlgae
Major Roles of Bacteria in Plant NutritionMajor Roles of Bacteria in Plant Nutrition
FixationFixation • Symbiotic ( with legumes )Symbiotic ( with legumes )• Nonsymbiotic ( without legume )Nonsymbiotic ( without legume )
TransformationTransformation • Mineralization (organic N to NHMineralization (organic N to NH44++
))• Nitrification (NHNitrification (NH44
++ NO NO22-- NO NO33
--
ammonium nitrite nitrateammonium nitrite nitrate
• Denitrification(NODenitrification(NO33-- N N22OO-- or N) or N)
nitrate nitrous nitrogennitrate nitrous nitrogen oxideoxide
OxidationOxidation • Elemental and organic SElemental and organic S S SOS SO44
2-2-
sulfur sulfatesulfur sulfate
Regular Additions of Organic Residues Must
Be Made to Maintain Soil Organic Matter Levels
ORGANIC MATTERORGANIC MATTER
TEMPERATURE
RAINFALL
AMOUNT OF RESIDUE
=% SOIL
ORGANICMATTER
Soil ColloidsSoil Colloids
• Chemically active fraction
• Made up of colloidal & colloidal-like particles– organic matter– clay
• Colloids and clays develop electrical charges (+,-) as they are formed
• Predominant electrical charge most clays and organic matter is negative (-)
Ca2+
Ca2+
K+
Mg2+Al3+
K+
Mg2+
Kaolinite ParticleSoil colloids may be
envisionedas a huge
anion
Soil colloids may be
envisionedas a huge
anion
Cation ExchangeCation Exchange
Ca + 2H+
HH
+ Ca2+
Cation Exchange Capacity of Clays &
Organic MatterCation Exchange Capacity of Clays &
Organic Matter
Clay MineralExchange Capacity
cmol(+)/kgKaolinite 3-5
Montmorillonite 100-120
Vermiculite 100- 180
Illite 40
Organic Matter 200-400
pH is a term used to describe the H ion (H+) activity and/or
concentration in solution
pH = -log (H+)
6
3
1
7
8
9
10
Sorensen pH ScaleSorensen pH Scale
12
13
14
11
5
4
2
0
Scale ranges from 0 to 14.
A pH of 7.0 is neutral meaning the hydrogen ion and hydroxyl ion activity are equal
pH values less than 7.0 are acidic
pH values greater than 7.0 are alkaline
pH ExpressionspH Expressions
pH of SolutionHydrogen ion activity,
g/liter
9.0 (strongly alkaline) 10-9 (0.000000001)
8.0 (moderately alkaline) 10-8 (0.00000001)
7.0 (neutral) 10-7 (0.0000001)
6.0 (moderately acidic) 10-6 (0.000001)
5.0 (strongly acidic) 10-5 (0.00001)
4.0 (very strongly acidic) 10-4 (0.0001)
Soil pH Reflects Hydrogen Ion ActivitySoil pH Reflects Hydrogen Ion Activity
Soil pH
Acidity/Alkalinity Compared to
pH 7.0 9 100
8 10
7 Neutral
6 10
5 100
4 1000
Soil pH
Acidity/Alkalinity Compared to
pH 7.0 9 100
8 10
7 Neutral
6 10
5 100
4 1000
Alkal
inity
Acidi
ty
Sodic soils
Calcareoussoils
Humid regionarable soils
Forestsoils
6
5
4
7
8
9
10
Pure waterMilk
Natural rain
BeerCoffee
Bicarbonateof soda
Milk ofmagnesia
Range found in common products
pH of Common Products & SoilspH of Common Products & Soils
pH scaleRange foundin various soils
Soil pH is one of the most important chemical
reactions that occurs in soils
Why?
It affects so many reactions and activities
that occur in soils
• Chemical Reactions
• Nutrient
Availabilitydisk 10
• Toxic Elements in Soils
• Al and Mn
• Toxic Elements in Soils
• Al and Mn
• Toxic Elements in Soils
• Al and Mn
• Toxic Elements in Soils
• Al and Mn Disk 11 Gary
53
89
100
0
10
20
30
40
50
60
70
80
90
100
Rel
ativ
eE
ffic
ien
cy ,
%
5 6 6.5
Soil pHw
Relative Nitrogen Efficiency
34
75
100
0
10
20
30
40
50
60
70
80
90
100
Rel
ativ
eE
ffic
ien
cy ,
%
5 6 6.5
Soil pHw
Relative Phosphorus Efficiency
52
100 100
0
10
20
30
40
50
60
70
80
90
100
Rel
ativ
eE
ffic
ien
cy ,
%
5 6 6.5
Soil pHw
Relative Potassium Efficiency
Soils Become Acid Because- Soils Become Acid Because- • Developed in areas with high rainfall, resulting
in:
a. leaching and plant uptake of base forming cations (Ca2+, Mg2+, and K+)
b. rapid reaction of water with Al & Fe, which produces H ions
• Application of acid forming fertilizers – mostly those containing ammonical (NH4
+) nitrogen
• Decomposition of organic matter
• Microbial activity
Nitrogen Conversion in the Soil Produces AcidityNitrogen Conversion in the Soil Produces Acidity
Organic Matter Manure, etc.
NH4 - N FertilizerSources
2 NH4+ + 4O2
Bacteria 2NO3
- + 2H2O + 4H+
Note: The H+ is theacidity component
Determining Soil AcidityDetermining Soil Acidity
• pH Kits
• pH Meters
• pH Kits
• pH Meters
Determining Soil pH & Limestone Requirement at UGA Laboratory
• Automated soil pH analyzer (130 samples can be analyzed per hour)
• Two analyzers operational gives the Lab capacity to analyze 260 samples/hour for pH and lime requirement
• Soil pH is recorded on soil test report as pHCaCl2 and Equivalent Water pH along with the lime buffer capacity.
Note these pH values are equivalent to 5.4 and 5.9 for pH determined in calcium chloride
Desired pH for Some CropsDesired pH for Some Crops
5.0 – 5.5* 5.5 – 6.0* 6.0 – 6.5*
Blueberries Sweet Potatoes Sweet Corn
Irish Potatoes Lawn Grasses Tomatoes
Azaleas Annual Flowers Onions
Rhododendrons Perennial Flowers Cabbage
Spring Flowering Bulbs
Watermelon
*pHw Values
How Can We Reduce Soil Acidity?
Apply Liming Materials
Lime Sources and Their Relative Neutralizing Values
Lime Sources and Their Relative Neutralizing Values
Liming Material Relative Neutralizing Value*
Calcitic Limestone 85 – 100
Dolomitic Limestone 95 - 108
Burned Lime 179
Hydrated Lime 120 - 135
Gypsum None
*Calcium Carbonate is used as a standard with a neutralizing value of 100
Incorporate Lime for Best Results
FREQUENCY AND RATE OF LIMING DEPENDS ON:
FREQUENCY AND RATE OF LIMING DEPENDS ON:
• SOIL pH
• SOIL TEXTURE
• NITROGEN FERTILIZATION RATES
• REMOVAL OF Ca AND Mg BY PLANTS
• AMOUNT OF LIME PREVIOUSLY APPLIED
• SOIL pH RANGE DESIRED
• SOIL pH
• SOIL TEXTURE
• NITROGEN FERTILIZATION RATES
• REMOVAL OF Ca AND Mg BY PLANTS
• AMOUNT OF LIME PREVIOUSLY APPLIED
• SOIL pH RANGE DESIRED
Acidifying SoilsAcidifying Soils
• Acidifying soils is frequently required in nursery and horticultural situations.
Materials Used for Acidifying Soils
• Elemental sulfur
• Aluminum sulfate (Alum)
• Iron sulfate
Reducing Soil pH with Sulfur or Aluminum Sulfate
Reducing Soil pH with Sulfur or Aluminum Sulfate5.5 6.0
Initial Soil pHw
Textural Classification
Sandy Loamy Clayey Sandy Loamy Clayey
Sulfur Required, lbs per 1000 ft2**
5.5 0 0 0
6.0 4 10 16 0 0 0
6.5 8 20 32 4 10 16
7.0 12 29 47 8 20 32
7.5 15 38 61 12 29 47
**Aluminum sulfate rate = lbs. Sulfur x 6
Reducing Soil pH with Sulfur or Aluminum Sulfate
Reducing Soil pH with Sulfur or Aluminum Sulfate4.5 5.0
Initial Soil pHw
Textural Classification
Sandy Loamy Clayey Sandy Loamy Clayey
Sulfur Required, lbs per 1000 ft2**
5.0 4 10 16 0 0 0
5.5 8 20 32 4 10 16
6.0 12 29 47 8 20 32
6.5 15 38 61 12 29 47
7.0 19 48 77 15 38 61
7.5 23 57 92 19 48 77
**Aluminum sulfate rate = lbs. Sulfur x 6
• Elemental sulfur and sulfur compounds are the most popular acidifying materials.
• Bacteria are required for this process to occur.
– 2S + 3O2 + 2H2O2H2SO4 (Thiobacillus)
• Aluminum and iron sulfates can also be used
• These materials are very effective but are sometimes difficult to find
• They react quicker and do not require microbial oxidation
• Acidity is result of hydrolysis reaction:– Al2(SO4)3 + 6H2O 2Al(OH)3 + 6H+ + 3SO4
=
– Fe2(SO4)3 + 6H2O 2Fe(OH)3 + 6H+ + 3SO4=
Thank You